The Research On Highly Accuracy Aspheric Surface Testing Based On Computer-Generated Hologram

Compared with the traditional spherical surface,the aspheric surface can not only improve the relative aperture of the system,expand the field of view of the system,improve the performance of optical systems effectively,but also simplify the system structure and reduce the system volume,has been used in the current optical system design widely.In order to achieve the expected results of the optical system,high-precision aspherical surface fabrication is particularly important.High-precision surface testing technology and high-precision processing technology of aspherical are complementary,so the technology of testing high-precision aspheric surface has become a hot topic and frontiers of optical research.For the commonly used large aspheric surfaces,the traditional testing methods such as the three-coordinate measurement,the processing surface method can not meet the requirements.Computer-generated hologram(CGH)is an interferometric measurement,which can generate phase compensation of the ideal wavefront required for any aspheric surface.It corresponds to the surface to be tested by mathematical expressions,and does not need to be cross-checked by two pairs.Besides,it has simple structure and auxiliary adjustment function,which can precisely adjust the relative position with the surface to be tested.In summary,the testing technology of aspheric surface based on CGH has unparalleled advantages in aspheric testing,and in-depth research on is conducive to improving the processing quality and promoting the application of aspheric surfaces.Firstly,the paper introduces the research status of the testing of aspheric surface based on CGH,enumerates several aspheric surface testing methods,clarifies the advantages of CGH in the testing of large aspheric surface.Discourse the theoretical basis of spherical and the principle of CGH testing method of aspheric surfaces.Illustrate the design method and flow of CGH.Secondly,select appropriate type of CGH based on the different working modes of CGH in the optical system,simply the CGH to the binary grating linear model,analysis the influence of various processing parameters of CGH on the diffraction efficiency and the testing result based on the model using Matlab.The processing parameters of the CGH designed in this paper are clarified,select appreciate layout of CGH in accordance with the surface.It is finally determined that the primary holographic part of CGH designed in this paper uses first-order diffracted light while the auxiliary holographic part uses three-order diffracted light.Each part of the hologram is distributed in a fan-shaped annular band shape,and the duty ratio is 0.5 and the etching depth is 0.35 ? ?Then the main hologram of the coaxial aspheric surface(D=600mm,K=-1.1097,R=1200mm)is designed,the method for determining the initial structure of the system is given.Analyze the influence of the ghost image of the high-order diffracted light on the imaging result,the different diffracted orders are separated by adding the carrier frequency to reduce the ghost image interference.Comprehensively considering the imaging quality and processing difficulty,the main holography of the coaxial aspheric surface testing system is ultimately obtained.The design result indicates that the RMS value is 0.0001 ? and the minimum density is 14.5?m.The auxiliary holography is designed based on the result of the structure of the main holographic system.The design residual of the system is 0 and the minimum density is 3.6?m,Therefore,the imaging quality of the system is high and the processing difficulty is few.The main hologram of the off-axis aspheric surface(D=410mm,K=-1.5614,R=5386.79mm)is designed performing the method of the CGH of coaxial aspheric.Analyze the drawbacks of this method,proposes a method of moving and rotating the off-axis aspheric surface to achieve the off-axis aspheric coaxial testing,which overcomes the adverse effects brought by the direct application of the coaxial CGH design method.Finally,the tolerance analysis and the experimental verification of the CGH testing system is carried out.According to the flow of processing CGH,the influence of the processing tolerances of CGH on testing accuracy are quantitatively analyzed by using the binary linear grating model mentioned above,the tolerances carried by defocusing and tilting are analyzed by ZEMAX.According to the design result,the testing system based on CGH is built to test the coaxial aspheric surface.The result is basically consistent with the result of offner compensation mirror which proves the feasibility of the system design.The method of system tolerance suppression is proposed.It is determined that the comprehensive error of the improved system is small and the testing accuracy of the system can reach 0.01 ? RMS.